1. Field of the Invention
The present invention relates to a constant voltage generating circuit.
2. Description of Related Art
FIG. 10 is a circuit diagram showing an example of conventional constant voltage generating circuits. A constant voltage generating circuit 200 of the present conventional example includes an ED-type reference voltage supply 210 and a buffer amplifier 220. The ED-type reference voltage supply 210 has a simple circuit configuration formed by using a depletion-type N-channel-type metal-oxide-semiconductor field-effect transistor (NMOSFET) 211 and an enhancement-type NMOSFET 212, and generates, with such a simple circuit configuration, a predetermined constant voltage Vreg that is insusceptible to variations in factors such as power supply and temperature.
An example of conventional arts related to this is disclosed in Japanese Patent Application Publication No. 2011-029912.
However, the ED-type reference voltage supply 210 is deficient in current supplying ability, and thus is not able to supply sufficient amount of current to a load 300. As a countermeasure to this problem, it has been a common practice to provide a buffer amplifier 220 having a high current supplying ability on a stage following the ED-type reference voltage supply 210, but this has disadvantageously invited an increase in circuit scale.